The present invention relates to an improved device for carrying injection molded plastic articles from a mold and for cooling said plastic articles while they are being carried. The invention further relates to improved means for ejecting or removing the plastic articles from the device.
The practice of removing injection molded plastic articles, such as PET preforms, from a mold by means of cooled tubes mounted on a robot take-off plate is well known in the art. U.S. Pat. Nos. 4,729,732 to Schad et al. and Re. 33,237 to Delfer exemplify two of the known take-off systems.
In the system shown in the Schad patent, a robot takeoff plate is carried by the molding machine and inserted between the platens defining the molding station when the platens are in a mold open position. The take-off plate has attached thereto a number of open ended hollow tubes for receiving parisons molded by the molding machine. The number of tubes associated with the plate is determined by the number of parisons molded by the machine during a single molding cycle. Each of the tubes for holding the parisons is connected at its base to a suction or vacuum source. The suction or vacuum is used to remove the parisons from the molding machine and to hold them in place in the tubes during transfer to a receiving station. After the take-off plate has been moved out from between the platens forming the molding station, it is rotated to a position adjacent the receiving station. The parisons are then delivered to pallets at the receiving station by releasing the suction or vacuum. The parisons are positioned in the release mode so that their open neck portions engage plugs supported by a frame on the pallets.
The Delfer patent shows an approach similar to Schad's for removing molded articles, such as parisons, from a molding machine. As shown in FIG. 3 of the Delfer patent, the robot take-off plate has a number of open ended tubes embedded therein for receiving the molded articles. Again, the number of tubes present in the plate is determined by the number of molded articles produced during a single molding cycle. Each of the tubes is connected to a suction or vacuum source and/or a pressurized fluid source. The vacuum is used to retain the molded articles in the tubes, while the pressurized fluid is used to eject the molded articles from the tubes. The plate also has a series of cooling passages for cooling the plastic articles held in the tubes. The cooling passages may contain a circulating cooling fluid.
The principal disadvantage of these systems is that should one of the molded articles stick in its tube while the others are successfully ejected, there is typically insufficient air or fluid pressure in the sticking tube to eject the stuck article. This is because all of the other empty tubes provide an open vent to discharge most of the available compressed air or fluid.
Mechanical devices to eject molded articles from a take-off plate have also been used in molding systems. For example, a mechanical take-off plate ejector device used by Krupp has been illustrated in Plastics Technology, September, 1989, pp. 39-40. In the Krupp machine, mechanical knock-out pins are provided in each tube. The pins are mounted on a common ejector plate behind the main take-off plate. Actuation of this ejector plate effects simultaneous ejection of all molded articles or preforms within the carrying tubes. The disadvantage of this approach is the additional space required to accommodate the ejector plate. As a result of the presence of the ejector plate, the mold open stroke must be increased to allow the thicker tooling plate assembly to enter between the open mold halves to pick up the preforms. The additional opening and corresponding closing stroke thus required penalizes the molding cycle time. A second disadvantage to this device is the increased weight caused by the ejector plate, the individual pins, and the plate's actuation mechanism. This additional weight reduces the robot's drive mechanism's ability to move the plate assembly quickly in and out of the mold and consequently penalizes the molding cycle time further.
Another mechanical approach has been employed in some molding machines manufactured by the assignee of the instant application. This mechanical approach involves placing a sliding plug in each of the tubes used to receive the molded articles, preforms or parisons. In the loading position, the plug is retracted by the vacuum pulling the molded article into the tube. A ball check is provided to maximize the vacuum flow. When the vacuum is replaced with a positive air pressure, the ball check is closed to limit the air loss if some of the molded articles stick in the tubes. The plug is blown forward by the air pressure to push out the cooled molded article within the tube. Unfortunately, this approach did not completely or satisfactorily solve the problem of molded articles sticking in the tubes.
In view of the foregoing problems, the inventors set out for themselves the principal object of providing an improved system for carrying molded articles, for cooling the articles while they are being carried, and for ejecting the molded articles from this robot take-off plate.
It is also an object of the present invention to provide an ejection system for which there is no increase in the overall size of the tooling or take-off plate assembly.
It is still a further object of the present invention to provide an ejection system as above which does not increase the mold stroke or the molding cycle time.
Still other objects and advantages of the present invention will become more apparent from the following description and drawings wherein like reference numerals depict like elements.